Certain subterranean geologic formations contain significant reservoirs of natural gas. For example, the Marcellus Shale subterranean formation, which extends from central and western New York southwardly through Pennsylvania, West Virginia, and eastern Ohio, contains significant natural gas deposits. Extraction of this gas has been made economically and technically feasible by the utilization of a technology referred to as hydraulic fracturing, commonly abbreviated as “hydrofracking,” or “fracking.” This technology utilizes injection of large volumes of water at high pressure to fracture the subterranean shale structures, which causes them to separate and release the pockets of methane gas contained within the shale strata.
During the drilling of the wells, drilling mud and treated water are utilized for lubrication, suspension of drilling wastes, and as weighting agents to form a plug to restrain the pressure of the natural gas within the well bore. This drilling operation produces a waste effluent stream referred to as “pit water.” This pit water is the liquid and semi-solid remnants resulting from the drilling process typically remaining after the bulk of the rock cuttings have been removed by conventional means. This pit water contains contaminants in the form of drilling mud, pulverized rock cuttings and chemicals from the subterranean structures, as well as from pretreatment of the water with certain chemicals prior to performing the drilling along with other debris. As much as one hundred thousand gallons of pit water may be generated from the drilling process for each well. Separation of the rock cuttings and drilling muds from this water is needed.
The contaminants in this water render it unsuitable for reuse except in small proportions. Disposal of the water and the organically contaminated solids contained therein has become an expensive proposition for the well developers and also a difficult environmental problem. Treatment of the water with solidification additives is sometimes used. New environmental regulations, as well those proposed and likely to be implemented, may severely limit the ability to dispose of or treat this water by conventional means within the states of Pennsylvania and New York as well as Texas, and Idaho among others, and some foreign countries. There is a significant need by the well developers for technologies which will treat the water to enable its reuse to a maximum extent, and for the cost effective and environmentally satisfactory disposal of the contaminants contained in it.
The contaminants in this water include many of the following components:                Sodium chloride.        Calcium and magnesium (hardness) salts, typically in the bicarbonate and/or chloride form.        Soluble sulfate salts.        Volatile organic compounds (VOC) resulting from the degradation of the ancient sea creatures captured within the shale formation. (The VOCs may include small amounts of crude oil.)        Residual organic compounds (ROC) from the water treatment chemicals introduced into the drilling water to enhance the drilling process.        Pulverized rock cuttings.        Bentonite clay which may be a component of the drilling mud.        
The following are also possibly present, but to a lesser degree:                Barium salts, typically in either the soluble chloride form or the insoluble sulfate form, which may be a component of the drilling mud or contained with the rock cuttings.        Strontium salts, typically in either the soluble chloride form, or the insoluble sulfate form which may be component of the drilling mud or contained with the rock cuttings.        
Common practice may provide for some reuse of the pit water in limited quantities as makeup water for hydro-fracturing water or other drilling operations, provided that the pit water is from a “water based” drilling mud operation and it is clarified through sedimentation, and the soluble contaminants levels are below predetermined limits. Alternatively, previous disposal of the pit water has been accomplished by transport to and subsequent treatment at conventional municipal waste water treatment facilities and specialized industrial treatment facilities, provided that the drilling muds utilized are “water based.” New and pending regulations may severely limit this option. “Oil based” drilling mud may not be treated in significant quantities in conventional municipal waste water treatment facilities. In fact, there are considerable limitations to the disposal of “oil based” pit waters altogether. Most of these pit waters are treated with thermal technologies, bio-remediation, deep well injection, addition of solidifiers (such as polymers, sawdust, wood chips, lime, or vermiculite) and/or evaporation of the water fraction followed by landfill disposal of the remaining contaminated solids.
The sodium chloride is not considered a significant problem relative to the reuse of the water up to some practical limit that is determined by the drilling operator.
The soluble barium and strontium salts, and alternatively the soluble sulfate salts, form insoluble solids during and after the fracking process, which have been determined to be degradative to the drilling and/or hydrofracturing process when these materials exceed certain levels which depend upon the particular operator of the drilling rig. Elevated levels of these salts limit options for disposal as well. The soluble calcium salts form hardness scale in the subterranean shale structures and are similarly limited in concentration but at higher levels. Both of these conditions may result in the obstruction of portions of the fissures within the shale strata created by the fracking process when the water is reused, if the concentrations of these salts contained in it are excessive. The presence of the residual or incipient volatile organic chemicals in the return water results in further difficulties in proper reformulation of it as fracking water for reuse. The pulverized rock cuttings and residual mud present in this pit water represent suspended solids which are unacceptable in hydrofracking or drilling fluids.
The removal of certain suspended solids in the waste water from water based drilling mud is defined in various documentation and literature. The solidification of the salts may be accomplished by conventional evaporation technology, gelatinizing of the solution, or precipitation means. The current method of return water remediation is to transfer it upon its discharge from the wellhead into tanker trucks or pits, decant any clarified supernatant following settling or treatment for reuse, and then transfer the unusable remaining water and/or sludge into tankers. The tankers of sludge are then hauled substantial distances to off-site municipal or industrial water treatment plants, or to other solidification pits where further solidifiers may be added. This is expensive, and additionally, it may soon be prohibited in many jurisdictions (particularly New York, Pennsylvania and Texas) by new environmental regulations.
The aforementioned U.S. patent application Ser. Nos. 12/914,072 and 60/255,504 of Miller provide for a modular, portable and cost effective method and apparatus for treating the frack water for the removal of the barium, calcium and strontium salts onsite at the wellhead. However, there remains a need for a modular, portable, and cost effective method and apparatus for treating waste water produced from the utilization of oil-based drilling mud. The separation of the settleable and finely dispersed suspended solids from the aqueous phase must be accomplished in a manner such that the solids may be disposed of separately, and the water may be reused. It is desirable that the process and apparatus also accommodate the presence of any residual or volatile organic chemicals, typically including finely dispersed or emulsified diesel oil or other “oil” components of the drilling mud formulation, or natural crude oil component brought up from the wellhead; and residual soluble precipitate-forming salts as well.